Basically, graphene is a two-dimensional (2D) material with exceptional properties. Graphite consists of multiple layers of graphene. Graphene is increasingly of interest for use in a number of applications, such as in flexible electronics, semiconductors and as strengthening agents in advanced materials. This is because graphene possesses a number of unique and desirable properties, including being transparent, strong, light, and represents an excellent conductor of heat and electricity due to ultrahigh electrical and thermal conductivities and outstanding mechanical properties. These properties make it a promising material especially for applications such as for use in sensors, in transistors, in detectors, in advanced batteries, in supercapacitors and for many further non-electronic applications.
Due to the increasing number of possible applications, the market of graphene is a fast growing market with a rapidly rising demand. In general, the market trend is changing towards large-size production. And the technical requirements focus on lower sheet resistances, because Organic Photovoltaic (OPV) devices and Organic Light-emitting Diodes (OLED) are entering the market. So methods suitable to provide large quantities of high quality graphene and related materials are urgently required. However, the large-scale production of graphene becomes a bottleneck in developing graphene and related materials. Various synthesis techniques including bottom-up and top-down methods have been developed and exploited to prepare such materials including materials with various graphene layers, dimensions, shapes, which leads to different qualities of resulting materials. Each of which have various advantages and disadvantages.
Although usual top-down processes like mechanical and chemical exfoliation of graphite or graphite oxide enables the synthesis of graphene related materials on a large scale, the number of graphene layers cannot be sufficiently controlled and although graphite oxide can be reduced to remove the functional groups, this is inevitably accompanied by a number of defects. Further, those methods usually suffer from a low efficiency. For example, production of graphene via steam and metal etching of graphene oxide requires a number of reaction steps and is time consuming with low efficiency and not suitable for large scale fabrication. In particular, the electrical conductivity of the final graphene and graphene related material is limited due to a resulting significant proportion of oxide groups and defects with detrimental effects on the electronic, optical and mechanical properties of the material. So this method can't meet today's requirements either. Dry exfoliation is usually time consuming and does not allow for large scale production, too.
Furthermore, the above processes are quite complicated. In comparison, few-layer graphene films have been produced via bottom-up processes like chemical vapor deposition on copper foils and films. Although this method can produce high quality graphene and related materials, its large-scale production is limited due to high energy consumption, high costs and many resulting defects which might affect the electrical conductivity of the resulting materials. Production of graphene by epitaxial growth is significantly limited by high quality substrate requirements, high temperatures of usually more than 200° C. up to more than 1200° C. and harsh conditions.
For example, U.S. Ser. No. 14/539,269 discloses a method of preparing graphene and graphene related materials, respectively, comprising exposing a highly crystalline carbide to a halogen-containing gas at temperatures of at least 200° C. to 1200°, treating the resulting carbide-derived carbon with an acid to form carbon oxide and subsequently reducing the carbon oxide. CN104843677 refers to a method of manufacturing a graphene related material, wherein graphite is dispersed in water with chitosan and acetic acid. Chitosan acts as the chemical for exfoliation. CN103663438 discloses a method of manufacturing a graphene and graphene related materials, respectively, starting from graphite oxide comprising dispersing obtained graphene oxide with sonication in the presence of a strong acid. The resulting product is porous graphene oxide which needs to be reduced in a further reaction step. It is evident that such methods require a number of reactions steps and are time consuming, not environmentally friendly and/or need expensive materials, equipment and harsh conditions or they do not provide graphene and related materials with sufficient quality.
There remains a strong need for a production process that is capable of producing large volumes of high quality graphene and/or related materials suitable for large scale industrial production which meet today's or future's requirements and a strong need for respective resulting graphene and/or related materials.